No need to fertilize bougainvillea in this climate at this time of year

Q . Before the first freeze in Las Vegas what should I feed my bougainvillea? I have three plants, all in the ground. They are 6 years old and I wrap their bases before the freeze. They always come back come March and bloom beautifully August through October.

A. I like your idea of wrapping the bases of the plants before any freeze. That winter freeze is likely to occur from the first week of December to the first week of March.

Unless you have a very warm microclimate in your yard, and there are some in Las Vegas, you will see damage to them at the first light freeze with temperatures below 32° F.

Wood mulches also will protect the base of bougainvillea but wrapping it is more effective. This way when it freezes it will kill the top of the bougainvillea to the mulch or wrap and not much further.

Of course this works to temperatures below freezing for short periods of time. If the temperatures are extremely cold or at these temperatures last a long time that it may freeze the plant to the ground.

How well you protect the base of the plant will determine how strong it will come back, or not, next spring. Having bougainvillea in the spot in the yard that does not have a lot of wind and is close to a warm, south or even better yet, west-facing wall will improve its chances for survival.

Plants that freeze to the ground will come back like gangbusters next spring because of their established root system. Plants that are planted in the spring have to grow both the roots and the tops and so growth is divided between the two.

Plants that have an established root system only have to grow the top back and so all of that growth goes to top growth and we see huge amounts of growth in the spring.

You do not want to feed them anything this time of year. This goes for any winter-tender plant. These plants should get no fertilizer applied to them any time after mid-August. Fertilizers that stimulate new growth will cause the plant to become more succulent and lower its chances of surviving winter freezes.

This is not true of plants that have no problem surviving winter freezes. In fact, those plants can receive midfall applications of fertilizer with no problems. A midfall application of fertilizer can substitute for a spring application but not for winter-tender plants.

Q. I planted horseradish this fall. It’s growing nicely for a first-time grower I think. I have six nice big leaves coming off the plant. I was wondering when it’s ready for harvest. I’ve looked online, but most of the instructions involve spring planting and a fall harvest.

A. Horseradish does quite nicely here for a northern climate perennial but it needs time to develop its roots where we derive the spicy condiment. After the leaves have fully established, it will take two or three months, at a minimum, for harvestable roots.

It is in the mustard family where many members have spicy leaves and stems used in salads. This is perennial mustard so it sprouts from its underground rhizomes each year. The rhizome can be dug up in the fall or spring, divided and replanted again to create new plants.

In colder parts of the United States most planting is done in the spring. But here in the semi-south (actually we are in a “Transition Zone” climatically between north and south), we can plant a lot of things in the fall that are recommended for spring planting in the north.

You could plant during our entire winter if you are careful and have a warm microclimate, or create one, in your garden. Our real “winter” here is the summer months that are more brutal to plants than our winter.

If your plant got two or three months of good growth before fall I would’ve told you to harvest it, divide the rhizome and let it heal and then replant. Now that we are in the second week of November I think it is a little dangerous to recommend that unless you have that warm microclimate I was talking about.

I would wait until February to mid-March to dig it, divide the rhizome if it needs dividing, let it heal for 48 hours and replant it. If the rhizome has not given you enough growth for it to be divided, then I would just replant it.

Horseradish is a tough plant. In some parts of the country it is so tough it can be invasive in the garden. Any little section of the rhizome left in the ground after digging can create new plants. So you do not need a big part of that rhizome to start a new one.

There are some crucial gardening tips that you need to follow when planting or replanting horseradish or any plant started from rhizomes. Make sure the knife you use when dividing the rhizome is clean and sanitized. The cuttings you prepare for replanting can be anywhere from 3 to 6 inches in length.

Plant the rhizomes horizontally about 2 inches deep and about a foot apart. Don’t plant until all fresh cuts, or any damage to the rhizome, has had time to heal.

Heal the rhizomes by placing them in a warm spot (warm compared to outside, 60F or so) for 48 hours. This will allow any cuts or damage to begin to suberize or begin the healing process.

Be careful not to re-damage the rhizomes when planting. Those parts of the rhizome that recently healed can be damaged easily.

Make sure the soil has been prepared with good quality compost to a depth of 18 inches. Horseradish likes composted manure and prefers to be kept moist but not overly wet. It can survive drought conditions but is not productive.

It likes surface mulches 2 to 3 inches deep that keeps the soil moist and cool. You should dig them during the cool fall or spring months for harvesting and replanting for best flavor.

Use the large central root for cooking and the smaller, side roots for planting. Horseradish root will go bad very quickly after you start shredding or grating it for cooking. The root oxidizes quickly, which ruins the flavor.

Use it as soon as possible after harvest. Shredded or grated horseradish root can be stored in vinegar for short periods of time as this will help keep it from oxidizing. If you are storing it in the refrigerator, keep the roots moist and in long pieces until you need it.

It will probably store in the refrigerator for about 3 to 4 weeks in more humid areas such as the crisper. It can store longer than this but you would need more sophisticated storage than just a refrigerator.

Q. This question regards our bottle tree. Should we trim and shape the tree? It has grown to a considerable height. The wind, appearance, and health of the tree are our concerns. Does the cracking on the trunk need addressing? And should I wrap the trunk in winter?

A. It’s a very nice looking tree. I posted the picture you sent me on my blog. Personally, I would not do anything to it. The cracking in the trunk is normal for an aging tree. It should not have difficulty handling a normal winter.

I know it may not look picture perfect but that is what can be charming about these types of trees used in our environment. As it grows, it will naturally fill in some of the voids.

You could prune it to shape it a bit but be very careful when you do this and do not change it radically or the plant may respond in a way that you may not like.

Don’t do anything dramatic to it or you could end up with some problems such as sunburn on the lower limbs and, consequently, dieback.

If you are going to do some pruning, do it this winter and hire someone who has a good reputation with shaping trees. This tree is a focal point on your property and needs special care.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com.